The process for producing olefin compounds by gas phase dehydration reaction of alcohols is already known. For example, Patent Document 1 discloses a process for producing olefin compounds in which a secondary alcohol is subjected to dehydration reaction in a gas phase at a temperature of from 300 to 400° C. in the presence of zirconium oxide.
However, in the gas phase reaction represented by the method described in Patent Document 1, it is required to vaporize all of raw materials used therein. In particular, when using a high-boiling alcohol as the raw material, energy consumption of the process tends to become excessively large, resulting in disadvantages from the viewpoint of costs. In addition, upon olefination of the alcohol under high-temperature conditions, branching of olefins owing to alkyl rearrangement and polymerization of the olefins also tend to occur in the olefination reaction, thereby causing the problems such as poor yield of the aimed reaction product.
On the other hand, there is also known the process for producing olefin compounds in which an alcohol is subjected to dehydration as a liquid phase reaction using a homogeneous acid catalyst such as concentrated sulfuric acid and sulfonic acid. Meanwhile, the “liquid phase reaction” as used herein means such a reaction which is carried out at a temperature not higher than a boiling point of the raw alcohol, i.e., not higher than the temperature at which a liquid phase of the alcohol is still present. For example, Patent Document 2 discloses a process for producing olefin compounds in which a primary alcohol is subjected to dehydration in a liquid phase using trifluoromethanesulfonic acid as a dehydration catalyst.
However, the homogeneous acid catalyst used in the liquid phase reaction represented by the method described in Patent Document 2 is generally corrosive and therefore tends to cause elution of metal components from a reactor. In addition, the liquid phase reaction needs neutralization of waste catalysts, etc., resulting in disadvantages in view of costs. Further, in the olefination using a catalyst having a strong acid site, similarly to the above reaction under high-temperature conditions, branching of olefins owing to alkyl rearrangement and polymerization of the olefins also tends to occur in the olefination reaction, thereby causing the problems such as poor yield of the aimed reaction product.
From the above reasons, it has been demanded to provide a method for producing olefins by subjecting alcohols to dehydration at a low temperature and in a liquid phase using a solid acid catalyst.
However, it is generally known that when the dehydration reaction of alcohols is conducted under low temperature conditions, intermolecular dehydration of the alcohols preferentially occurs to thereby produce an ether. For example, Patent Document 3 discloses a process for producing diisopropyl ether in which isopropyl alcohol is reacted at a temperature of from 150 to 300° C. using a sulfonic group-containing ion exchange resin as a catalyst.
Thus, in the dehydration reaction of alcohols, both intramolecular dehydration and intermolecular dehydration of the alcohols tend to occur in parallel. In particular, when the dehydration reaction of alcohols is conducted at a relatively low temperature, the intermolecular dehydration preferentially occurs to thereby produce an ether. In consequence, it is considered that olefins are hardly produced at a low temperature in an efficient manner.